June 12, 2012

Aging Trees Lab

As a way to encourage scientific writing (which I would distinguish from writing about math/science) I've been doing quarterly lab reports.  Students experiment in geometry all the time: we make hypotheses, try them out, evaluate our data and come to conclusions.  Four times a year I'd like them to write up that process a bit more formally.  This was the first year I've done this and I'm still learning what the expectations are in the science department and how to translate that into math class.  For this last report I went with a fill in the blank format; next year I will probably start with this type of handout and hope that they can write their own report without the structuring by the end of the year.  Sometimes I have to work backwards to find the right amount of support, but we got there!

This lab was originally inspired by a heat wave and a never ending school year- we were studying circles and I needed a good reason to go outside.  Well, outside there are trees, which have roughly circular trunks.  I did some googling and discovered some wonderful scientists had done the research that would let us determine the age of several types of trees knowing only their circumference!  The biggest obstacle in this lesson turns out to be identifying the trees, not the math involved.  I narrowed the list down to 4 trees that grow along the path behind our school and provided detailed descriptions for identification.  Even when I started the class talking about how we were going to determine the age without hurting the tree, there would still be one kid who would run over to me with a leaf saying "What tree is this?!"  But I think that learning about nature, while out in nature, is really important.  So they examine the tree with the light bark and the toothed leaves, and then I give them a hint to look a few feet away to find the tree that has white bark and doubly toothed leaves.  Because yes, the white birch really is white!

Worksheet we use outside: (one per group)

Aging Trees by Circumference

Scaffolded lab report: (one per person)

Aging Trees Lab Report

Many thanks to Journey North for the original lesson, they provide more growth factors if the 4 I chose don't grow on your school grounds.  Note the comment on forest growth vs. pampered plants; that is what I was hoping students would think of when I asked for sources of error, but most everyone just said that maybe they measured wrong (the more experienced report writers attributed it to rounding error which sounds far more sophisticated).


  1. Am I correct that you did this with mid-high-schoolers? Do you think this would work with 6th graders? Thinking it could be a great extension to our work with circles!

    1. My students are in 10th grade but it is absolutely accessible to 6th graders. I hope they enjoy it!